1. Technical Field
The present invention relates to a display driver, a display controller, an electro-optical device, an electronic apparatus, and the like.
2. Related Art
Nowadays, electro-optical panels such as color liquid-crystal panels are often used in electronic apparatuses such as monitors, TVs, and notebook computers. In color liquid crystal panels, each pixel is constituted by R, G, and B subpixels, for example, and one pixel, as a whole, expresses one color by combining colors of the R, G, and B subpixels. The colors of the R, G, and B subpixels are each determined by the luminance of light that passes through a color filter provided thereon. The luminance of light that passes through each color filter is determined by a voltage supplied to a corresponding source electrode (data line) of the liquid-crystal panel. This voltage is referred to as a gray level voltage. The electronic apparatus is provided with a display driver including a circuit device that drives the liquid-crystal panel by controlling the gray level voltage.
In general, the input (such as an input voltage or an input signal) and the output (such as light transmittance or brightness) in the liquid-crystal panel are not in a linear direct proportional relationship. Each liquid-crystal panel has its own specific gamma characteristic (luminance characteristic) resulting from the liquid-crystal material that is used and variations in manufacturing. Therefore, gray level voltages in which consideration is given to the characteristics of the liquid crystal panel need to be supplied to the source electrodes of the liquid-crystal panel in order to express desired gray levels.
When gamma correction is performed by digital processing, a processing circuit of a display driver (or a processing circuit of a display controller) performs correction processing on display data input from an external device (CPU of an electronic apparatus, for example), and outputs corrected display data to a drive circuit. For example, the processing circuit stores correction data in a memory as a look-up table (hereinafter, referred to as an “LUT”), and performs gamma correction by making reference to the LUT.
The characteristics of a liquid-crystal panel are known to change greatly according to temperature. When there is a large change in temperature, temperature compensation processing for switching data (LUT to be referred to) used for gamma correction needs to be performed. In this case, if there is a large change in output gray level in a short period of time (drive voltage changes a large amount), a change in luminance to a degree that a user can recognize may occur, and therefore it is not preferable.
In JP-A-2009-294265, a method is disclosed in which a plurality of gray level regions are set, and gamma conversion processing is successively performed for each gray level region. Also, in JP-A-2009-294265, a method is disclosed in which gamma conversion processing is performed step by step such that the color difference ΔE is less than or equal to a predetermined value.
In JP-2015-176120, a method is disclosed in which the power supply voltage of drive voltages is increased or decreased step by step.
In the method in JP-A-2009-294265, control so as to perform gamma conversion for each gray level region, or control so as to limit the color difference ΔE due to gamma conversion to be less than or equal to a predetermined value needs to be performed, and a circuit for performing gamma conversion processing becomes complicated. Also, the method in JP-2015-176120 is a method in which analog gamma correction is performed so as to control the drive voltage, and is not a method in which gamma correction is performed through digital processing. Voltages need to be finely controlled, in analog gamma correction, in order to suppress a change in luminance or color (flickering in a screen) when temperature compensation is performed, and therefore the circuit becomes complicated.